Ordinarily, this does not consider the age of the species itself, comparing species by the range of age-span of their individuals, or the time between first appearance (speciation) and extinction of the species.

If the mortality rate of a species does not increase after maturity, the species does not age and is said to be biologically immortal. Many examples exist of plants and animals for which the mortality rate actually decreases with age, for all or part of the lifecycle.[1]

If the mortality rate remains constant, the rate determines the mean lifespan. The lifespan can be long or short, though the species technically "does not age".

Hydra species were observed for four years without any increase in mortality rate.[2]

Other species have been observed to regress to a larval state and regrow into adults multiple times.

The hydrozoan species Turritopsis dohrnii (formerly Turritopsis nutricula) is capable of cycling from a mature adult stage to an immature polyp stage and back again. This means no natural limit to its lifespan is known.[3] However, no single specimen has been observed for any extended period, and estimating the age of a specimen is impossible.

At least one hydrozoan (Laodicea undulata[4]) and one scyphozoan (Aurelia sp.1[5]) can also revert from medusa stage into polyp stage.

The larvae of skin beetles undergo a degree of "reversed development" when starved, and later grow back to the previously attained level of maturity. The cycle can be repeated many times.[6]

Various claims have been made about reviving bacterial spores to active metabolism after millions of years. Claims have been made of spores from amber being revived after 40 million years,[7] and spores from salt deposits in New Mexico being revived after 240 million years, the longest living organisms in history.[8][9] In a related find, a scientist was able to coax 34,000-year-old salt-captured bacteria to reproduce. His results were duplicated at a separate independent laboratory facility.[10]

A seed from the previously extinct Judean date palm was revived and managed to sprout after nearly 2,000 years.[11]

Silene stenophylla was grown from fruit found in an ancient squirrel's cache. The germinated plants bore viable seeds. The fruit was dated to be 31,800 years old ± 300 years.[12]

In 1994, a seed from a sacred lotus (Nelumbo nucifera), dated at roughly 1,300 years old ± 270 years, was successfully germinated.[13][14]

Around 1992, working among others with entomologist George Poinar, Cano sequenced the DNA of a fossil weevil trapped in amber[17]; Poinar was the author of a 1982 paper on conservation of specimens in amber[18] which influenced Michael Crichton to write his award-winning Jurassic Park.[19]

As with all long-lived plant and fungal species, no individual part of a clonal colony is alive (in the sense of active metabolism) for more than a very small fraction of the life of the entire colony. Some clonal colonies may be fully connected via their root systems, while most are not actually interconnected, but are genetically identical clones which populated an area through vegetative reproduction. Ages for clonal colonies, often based on current growth rates, are estimates.[20]

Pando is a Populus tremuloides (quaking aspen) tree or clonal colony that has been estimated at 80,000 years old.[21] Unlike many other clonal "colonies", the above-ground trunks remain connected to each other by a single massive subterranean root system.

The Jurupa Oak colony is estimated to be at least 13,000 years old, with other estimates ranging from 5,000 to 30,000 years old.[22]

A huge colony of the sea grass Posidonia oceanica in the Mediterranean Sea is estimated to be between 12,000 and 200,000 years old. The maximum age is theoretical, as the region it occupies was above water at some point between 10,000 and 80,000 years ago.[23][24][25]

Lomatia tasmanica in Tasmania: the sole surviving clonal colony of this species is estimated to be at least 43,600 years old.[26]

Old Tjikko, a Norway spruce in Sweden, is a tree on top of roots that have been carbon dated to 9,550 years old. The tree is part of a clonal colony that was established at the end of the last ice age. Discovered by Professor Leif Kullman, at Umeå University, the tree is located in the county of Dalarna in Sweden. Old Tjikko is small, only 5 m (16 ft) in height.[30][31][32][33]

Some endoliths have extremely long lives. In August 2013, researchers reported evidence of endoliths in the ocean floor with a generation time of 10 millennia.[37] These are slowly metabolizing, not in a dormant state.

A Great Basin bristlecone pine (Pinus longaeva) is measured by ring count to be 5067 years old.[38] This is the oldest known tree in North America, and the oldest known living individual nonclonal tree in the world.

The Cypress of Abarkuh is estimated to be between 4000 to 5000 years and is likely the second-oldest living being in Asia (or the oldest according to Russian scientist Alexander Rouf[citation needed]).

Llangernyw Yew may be the oldest individual tree in Europe and second- or third-oldest individual tree in the world. Believed to be aged between 4,000 years and 5,000 years old, this ancient yew (Taxus baccata) is in the churchyard of the village of Llangernyw in North Wales.

Fortingall Yew, an ancient yew (Taxus baccata) in the churchyard of the village of Fortingall in Perthshire, Scotland, is one of the oldest known individual trees in Europe. Various estimates have put its age between 2,000 and 5,000 years, although now believed to be at the lower end of this range.

Nonja, a Sumatran orangutan, died at the age of 55 years in December 2007. She was claimed to be the oldest-living orangutan of her species.[52]

The tuatara, a lizard-like reptile native to New Zealand, can live well above 100 years. Henry, a tuatara at the Southland Museum in New Zealand, mated for the first time at the estimated age of 111 years in 2009 with an 80-year-old female and fathered 11 baby tuatara.[53]

A female blue-and-yellow macaw named Charlie was reportedly hatched in 1899, which would make her 117 years old, as of 2016. Her age has not been independently confirmed and the claim may not be reliable. She is claimed to have formerly belonged to Winston Churchill, but Churchill's daughter denies the claim.[56]

Lin Wang, an Asian elephant, was the oldest elephant in the Taipei Zoo. He was born in January 18, 1917, and died in February 26, 2003, at 86 years, surpassing the previous record of 84. Normally, elephants live up to 50 years, while their maximum lifespan is generally estimated at 70.

The oldest living horse on record was named Ol' Billy. Bill was allegedly born in the year 1760 in London, England. Bill died in 1822 at the age of 62 years. Henry Harrison, an occupant of London during the time, had also allegedly known Ol' Billy for 59 years until Bill's death.[61]

Creme Puff, a cat owned by Jake Perry of Austin, Texas, was born August 3, 1967, and died three days after her 38th birthday on August 6, 2005.[62]

The oldest bear on record was Andreas, a European brown bear, living in the ARCTUROS bear sanctuary in northern Greece. He was at least 50 years old at the time of his death.

A specimen, "Ming" of the Icelandic cyprine Arctica islandica (also known as an ocean quahog), a mollusk, was found to have lived 507 years.[74] Another specimen had a recorded lifespan of 374 years.[75]

Greenland shark had been estimated to live to about 200 years, but a study published in 2016 found that a 5.02 m (16.5 ft) specimen was 392 ± 120 years old, resulting in a minimum age of 272 and a maximum of 512.[79][80] That makes the Greenland shark the longest-lived vertebrate.[81]

Some koi fish have reportedly lived more than 200 years, the oldest being Hanako, which died at an age of 226 years on July 7, 1977.[82][83]

In 2012, a sturgeon was caught in a Wisconsin river that was estimated to be 125 years old.[96]

A killer whale of the "Southern Resident Community" identified as J2 or Granny was estimated by some researchers to have been approximately 105 years old at her death in 2017; however, other dating methods estimated her age as 65–80.[97][98]

A Swedish man claimed that a European eel named Ale was 155 years old when it died in 2014. If correct, it would have been the world's oldest, having been hatched in 1859.[99]